1. Field of the Invention
The present invention relates to a differential pressure measurement and, in particular, to a differential pressure measuring system and a differential pressure measuring method.
2. Description of the Related Art
When an oil plant is controlled, it is required to measure a differential pressure of a fluid between the different measuring positions in the oil plant. In an earlier method for measuring the differential pressure disclosed in published Japanese Patent Application 2003-166890, Fabry-Perot interferometers are displaced on the measuring positions. An optical path difference between the Fabry-Perot interferometers changes, depending on the differential pressure. Therefore, the differential pressure is measured by detecting the change of optical path difference by light. However, the earlier method requires complex signal processing to identify the center of an interference fringe to detect the change of the optical path difference. Also, when the center of the interference fringe is identified, a reduction of an emission power of a light source and a reduction of a transmittance of an optical waveguide may occur. In this case, interference fringe amplitude is reduced. When the amplitude is reduced, it is difficult to distinguish adjacent bright portions of the interference fringe. Therefore, a measurement error may occur when the differential pressure is measured. Further, the light intensity may be changed by the drift of an optical axis of a light source or the fluctuation of the emission power of the light source. Such change of the light intensity does not relate to the differential pressure and causes the measurement error.